1. Field of the Invention
The present invention relates to valves and methods for use with tracheostomized patients.
2. Description of the Related Art
U.S. Pat. No. 4,759,356, the entirety of which is incorporated by reference herein, describes a tracheostomy valve unit. The valve unit is securable to one end of a tracheostomy tube assembly to regulate air flow through the tube. The valve unit remains closed when the tracheostomized patient exhales, and at all other times except when the patient inhales. When the patient inhales, the valve opens to allow air to flow through the tracheostomy tube to the patient's lungs.
An outer end of the valve includes a support to which a flexible diaphragm is secured. The diaphragm selectively seals the valve in response to the inhalation and exhalation of the patient. A rivet passes through the center of the diaphragm and the center of the support to secure these two components to one another. The rivet also seats the diaphragm against a seating ring on the support to preload the diaphragm and create an effective closure that maintains a positive, uninterrupted contact all along the seating ring at all times except when the patient inhales.
When properly manufactured, the tracheostomy valve unit described in the '356 patent is an effective apparatus for blocking outward air flow through the patient's tracheostomy tube, and for allowing inward air flow through the tube. However, the rivet must be precisely placed in order to preload the diaphragm and create the effective closure described above. If the rivet does not pull the diaphragm far enough toward the seating ring the diaphragm will not be properly preloaded and the valve will not be sealed at rest. On the other hand, if the rivet pulls the diaphragm too far toward the seating ring the diaphragm will be overloaded and will require too much pressure to open. In extreme cases the diaphragm may even wrinkle, which causes gaps to develop between the diaphragm and the seating ring. The gaps, of course, compromise the sealing ability of the diaphragm.
As described in the '356 patent, the process of placing the rivet involves a heat-staking step. “The effective length of rivet 20 is established during installation by blocking head 20a of the rivet with an adjustable support while at the same time heat-staking end 20c. Adjustment of the adjustable support then compresses rivet 20 and forms heat-staked end 20c, which mounts the diaphragm to support 16 and preloads diaphragm 18.” (col. 9, ll. 52-58) Unfortunately, the heat-staking is rather imprecise, as the position of the heat-staked end 20c is affected by the temperature of the heat-staking apparatus and the length of time that heat is applied to the heat-staked end 20c. These variables are difficult to control with the precision necessary to properly place the rivet every time. There is also a tendency for melted plastic to stick to the tip of the heat-staking apparatus, which further complicates control over the process. Thus, a high percentage of the tracheostomy valve units are rejected during the manufacturing process, which in turn raises the cost of manufacturing the valve units.